Conventionally, electrode plates for secondary batteries are known, which include a current collector plate and an active material layer formed thereon and containing at least an active material and a binder. For example, one positive electrode includes a current collector plate made of aluminum foil and a positive active material layer formed thereon and containing a positive active material such as lithium metal oxide and a binder such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR). One negative electrode, for example, includes a current collector plate made of copper foil and a negative active material layer formed thereon and containing a negative active material made of a carbon material and a binder such as PVDF, SBR.
Typically, an active material layer is formed by applying an active material paste prepared through dispersion of active material, binder, and the like in a solvent on a current collector plate, followed by drying of the coated film of this active material paste. However, as the coated film is dried, the binder migrates toward the surface of the coated film with the solvent as the solvent vaporizes from the surface of the coated film. Because of this, the active material layer after the drying step tends to contain more binder on the surface side and less binder on the current collector plate side when viewed in the thickness direction. An electrode plate with such an uneven distribution of binder is prone to a problem of lowered bond strength between the active material layer and the current collector plate.
As one countermeasure, Patent Document 1 proposes alternately repeating a coating step of applying an electrode coating liquid (active material paste) made of active material and binder mixed together on a conductive current collector plate and a drying step of drying the electrode coating liquid applied on the plate several times each to form an active material layer (see claims, etc. of Patent Document 1). It is taught that, by this method, the distribution of binder in the active material layer can be made less uneven.